# undefined vs underlined

> English confusable word pair

## The two words

### undefined
*adjective · frequency rank #27,687*
Lacking a definition or value.

### underlined
*verb · frequency rank #25,629*
simple past and past participle of underline

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/vs/undefined-vs-underlined